Effect of shearing on crystallization of palm oil-based fat blends

Abstract

The effect of shearing on the polymorphic behavior of palm oil-based fat blends with low (LT-Fat) and high (HT-Fat) trans-fatty acid contents during storage was investigated. A shear stress was applied to fat blends at 5°C or 10°C by the flat-crush method or after rapid or slow cooling by the syringe-extrusion method. The fat networks were evaluated by cryo-scanning electron microscopy (SEM), polarized light microscopy, and solid fat content measurement, and the polymorphic transition from the β'-form to the β-form under thermal thawing between 5°C and 20°C was investigated by X-ray diffraction. Transition to the β-form of LT-Fat with shearing was retarded compared with that without shear. SEM revealed that with shearing, LT-Fat built complex networks involving both fine reticulation and a tight structure, whereas without shearing, the structure was nearly uniform. These results suggest that the non-uniformly network achieved by shearing could suppress the localization of specific triacylglycerides, preventing transformation into the β-form.